Mix and match these cardio-sculpting workouts to melt fat—fast

What if we told you that you could get all the better-body benefits of a half-hour workout in just 8 minutes? Sound too good to be true? We thought so too—until we talked to the experts. The secret is supercharged, high-intensity interval training, a shorter but revved-up version of typical interval workouts. In fact, scientists are so excited about these new findings that the American College of Sports Medicine hosted a special session on the topic. Try one—or all—of our speedy routines, ranging from 8 to 20 minutes. In just 2 weeks, you'll see a fitter, firmer body. Keep it up to get a flat belly, slim thighs, and even drop a size this month—without dieting.

Why Intervals Slim FasterIntroducing short bouts of vigorous activity can speed up weight loss and cut your workout time by up to half or more. Australian researchers found that women who alternated just 8 seconds of high-intensity cardio exercise with 12 seconds of low-intensity activity for 20 minutes, 3 times a week, slimmed down faster than steady-paced exercisers who worked out twice as long. Those who did intervals lost up to 16 pounds, shrunk their bellies by 12% and their thighs by 15%, and gained, on average, 1½ pounds of metabolism-revving muscle in 4 months—without dieting.

Intervals increase calorie burn both during and after exercise, which helps you lose weight faster. They may also work on a biochemical level. Vigorous activity normally produces lactate, a by-product of the breakdown of carbs for energy that inhibits fat burning, says lead author E. Gail Trapp, PhD, exercise science researcher at the University of New South Wales, Australia. It appears that by doing supershort bouts, lactate production is reduced to blast fat more effectively. At the same time, interval workouts may increase adrenaline, a hormone that helps to burn belly fat.

The Expert: Craig Ballantyne, a Toronto-based exercise physiologist and strength coach who specializes in interval routines, designed the workouts.

The Workouts At A Glance:What you'll need: Supportive athletic or walking shoes (specifically running ones if that's what you're doing), watch with a second hand or timer, cardio machine for Workout #2.

What to do: Choose one of our supercharged high-intensity interval workouts--or mix and match them—and perform it 3 times a week on nonconsecutive days.

How to do it: During low-intensity portions, you should be able to easily carry on a conversation. When you kick it into high gear, push yourself to the point that talking is nearly impossible. "Research shows that just about anyone—including people with heart disease, diabetes, or obesity—can safely benefit from vigorous, short bouts," says Martin Gibala, PhD, professor of kinesiology at McMaster University in Ontario. If you have any health conditions or don't exercise regularly, check with your doctor before trying these routines.

When McMaster University researchers had adults do four 30-second sprints (that's just 2 minutes of intense exercise!) on stationary bikes with easy pedaling in between, 3 days a week, they doubled their fitness capacity (the strength of their heart, lungs, and arteries) after 6 weeks and reported feeling stronger, firmer, and more energetic in just 2 weeks.

Our 8-minute workout, based on this study, delivers the same powerful 2 minutes of vigorous activity but in shorter bouts—15 seconds each—so you can really give it your all for faster results. For variety and to work different muscles, try this routine using the Fat-Blaster Moves from Workout #3.

Minutes

Activity

0:00

Warm up, walking at a moderate pace

2:00

Sprint, running as fast as you can

2:15

Walk at an easy pace

2:45

Sprint

3:00

Walk

3:30

Alternate 15-second Sprint and 30-second Walk intervals 6 more times

8:00

Finish

Workout #2: 12-minute calorie burner

Here's an indoor alternative to the 8-minute routine that delivers the same fabulous results. You can use any cardio machine, including a treadmill, an elliptical, or a stationary bike. The session and intervals are slightly longer (12 minutes total with 20- and 40-second intervals) to allow time for the equipment to adjust to the different intensity levels.

Take it easy, decreasing speed, incline, or resistance so you're going at a comfortable, moderate pace

3:00

Rev it up

3:20

Take it easy

4:00

Alternate 20-second Rev It Up and 40-second Take It Easy intervals 7 more times

11:00

Cool down by going at an easy pace

12:00

Finish

Workout #3: 20-minute fat blaster

This high-energy plan, based on Australian research, will reshape your body in no time. The simple Fat-Blasting Moves (at right) make it doable almost anywhere. We've matched the interval ratio from the study, but the bouts are slightly longer (12 and 18 seconds) to allow you to transition between moves and still hit your peak effort level to burn maximum fat. Marching in place is an easy way to recover in between. For a challenge, try this routine alternating sprints and walking like in Workout #1.

Minutes

Activity

0:00

Warm up by walking around or marching in place

2:00

Jumping Jacks

2:12

March in place

2:30

Speed Skater

2:42

March in place

3:00

High Knees

3:12

March in place

3:30

Twist

3:42

March in place

4:00

Repeat above intervals 7 more times in the order listed

18:00

Cool down by walking around or marching in place

20:00

Finish

1. Jumping Jacks Yep, the ones you used to do in PE class. Go as fast as you can.

2. Speed Skater Stand with feet together, arms at sides. Jump to right, leading with right leg. Left leg follows and crosses behind right foot as you land. Simultaneously reach left arm across body as if trying to touch floor. Repeat to left. Jump side to side as quickly as possible.

3. High Knees Run in place as fast as you can, lifting knees out in front of you as high as possible. Swing arms at sides.

4. Twist Stand with feet a few inches apart. Hop and rotate knees to right as arms go to left, landing with knees bent. Repeat, twisting in opposite direction.